The preservability of drinks in PET bottles is reduced to an undesirably short period of time by the limited gas tightness of the bottle wall. This applies especially to the storage of carbonated drinks. Hence, various attempts have already been made for improving the gas tightness of the bottle wall by plasma coating, e.g. by applying a gas barrier layer of SiO2.
Such a method is known e.g. from US 2005/0233077 A1 in the case of which up to two PET bottles are arranged in a common processing chamber and evacuated through a respective contact pressure valve and a common line. For this purpose, the bottles are first positioned on the contact pressure valves, the processing chamber being connected to the interior of the bottles in the open condition of the valve. The valve is closed by pressing the bottle thereagainst and the processing chamber is thus sealed against the interior of the bottles. The evacuation of the bottles and of the processing chamber as well as the supply of process gas are controlled through separate valves in the lines.
U.S. Pat. No. 6,328,805 B1 additionally discloses a plasma processing plant in the case of which the processing chamber and the interior of the bottle are evacuated in common. A valve, which can be used for adjusting the differential pressure, is provided between the processing chamber and an area connected to the bottle interior. The control of the process gas supply is executed via a separate valve. The processing chamber can only accommodate one bottle at a time and is opened between the respective coating processes. The pressure difference adjusted with the aid of the valve thus ceases to exist.
EP 1 391 535 B1 additionally discloses a contact pressure valve which seals the interior of a bottle to be evacuated against the exterior of said bottle, when the bottle opening is pressed against said valve.